1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and more particularly, to a direct lighting type LCD without a color filter, in which three-color lights emitted from a plurality of light sources are directly incident on red, green, and blue liquid crystal subpixels sequentially disposed on a liquid crystal panel by using a lenticular lens array without the need of a color filter disposed inside the liquid crystal panel so that a color image having high resolution can be realized without the color filter.
2. Description of the Related Art
FIG. 1 is a cross-sectional view of direct lighting type LCD according to the related art. Referring to FIG. 1, the direct lighting type LCD includes a liquid crystal panel 20 in which a plurality of liquid crystal pixels 23 are disposed to adjust transmittance of light and to act as a light valve, and a backlight unit 10 which illuminates light on the liquid crystal panel 20.
The backlight unit 10 includes an assembly 11 of light sources including a cold cathode fluorescence lamp (CCFL) 11a, an external electrode fluorescence lamp (EEFL), a white light emitting diode (LED) or red (R), green (G), and blue (B) LEDs emitting R, G, and B lights, wherein the assembly 11 of light sources further includes a reflector 11b disposed under each of the light sources, and a plurality of optical sheets from which lights emitted from the light sources are reflected by the reflector 11b or are uniformly mixed and dispersed into a plurality of liquid crystal pixels 23.
Here, R, G, and B are abbreviations of Red, Green, and Blue, and hereinafter, refer to red, green, and blue without any indications.
The optical sheets includes a diffuser plate 12, a diffuser sheet 13, a condensing sheet 14, a reflective polarization sheet 15, and a protection film 16 so as to properly adjust a viewing angle and brightness.
The liquid crystal panel 20 includes a rear glass substrate 22, a front glass substrate 25, the plurality of liquid crystal pixels 23 disposed between the rear glass substrate 22 and the front glass substrate 25, R, G, and B color filters 24 disposed inside the front glass substrate 25, a polarization sheet A 21 attached to the rear glass substrate 22, and a polarization sheet B 26 attached to the front glass substrate 25, wherein these elements are main optical elements. Each of the liquid crystal pixels 23 is comprised of R, G, and B liquid crystal subpixels used to realize R, G, and B images. Each of the R, G, and B color filters 24 is disposed on the front surface of each of the R, G, and B liquid crystal subpixels.
A method of realizing color images in a LCD includes: disposing R, G, and B subpixels used to realize R, G, and B images and included in a liquid crystal pixel which is a minimum unit of a pixel; and disposing each of R, G, and B color filters on the front surface of each of the R, G, and B subpixels so that R, G, and B lights among white light emitted from a backlight can pass through each of the R, G, and B subpixels.
In the LCD, most power of the white light emitted from the backlight unit 10 is lost due to the polarization sheets 21 and 26, the R, G, and B color filters 24, and the aperture ratio of the liquid crystal pixels 23. Only about 5% to 10% of the white light generated from the backlight unit 10 is emitted out of the LCD. Thus, light energy efficiency of the LCD is very low as compared to other flat display displays. Thus, improvements in light energy efficiency of the LCD are conducive to reinforcing a competitive force and to reducing energy consumption of the LCD.
FIG. 2 is a plan view of the structure of each the R, G, and B color filters 24 disposed inside the front glass substrate 25 of the liquid crystal panel 20 illustrated in FIG. 1.
Referring to FIGS. 1 and 2, the plurality of liquid crystal pixels 23 are included in the liquid crystal panel 20 and act as pixels in minimum units that constitute a color image. A liquid crystal pixel 23 is comprised of three, i.e., R, G, and B liquid crystal subpixels that are used to realize R, G, and B images. The R, G, and B color filters 24 through which R, G, and B lights pass are disposed inside the front glass substrate 25 and are disposed on the entire surface of each of the R, G, and B liquid crystal subpixels so as to realize color images.
A black matrix 24d that absorbs light so as to prevent color crosstalk is disposed between the R, G, and B color filters 24a, 24b, and 24c disposed on the front surface of each of the R, G, and B liquid crystal subpixels. The R, G, and B color filters 24 are core elements in producing color images. However, about 30% of the white light when passing through the R, G, and B color filters 24 is transmitted through the R, G, and B color filters 24, and about 70% of the white light is absorbed into the R, G, and B color filters 24 and is lost. Thus, this loss is the most part of losses of light energy that is generated in the LCD.
The loss of light energy of the LCD includes about 50% in the polarization sheets 21 and 26, about 30-50% in the aperture ratio of the liquid crystal pixel 23, and about 70% in the R, G, and B color filters 24. Totally 90% or more light loss occurs and causes high power consumption in the LCD. The R, G, and B color filters 24 are core elements in producing color images but cause much light loss due to absorption.
In order to solve the problem, field sequential color (FSC) technology has been developed to increase light energy efficiency of the LCD. The FSC technology has been devised so as to remove color filters that cause much light energy loss. In the FSC technology, R, G, and B LEDs are used as light sources of a backlight, and display screen image signals are divided into R, G, and B image signals and then, when the R LED is turned on, the R image signal is transmitted to the liquid crystal panel, and when the G LED is turned on, the G image signal is transmitted to the liquid crystal panel, and when the B LED is turned on, the B image signal is sequentially transmitted to the liquid crystal panel at a high speed so that a viewer can see color images.
The FSC LCD technology achieved considerable improvements in technology. However, in the FSC LCD technology, the speed of a circuit for adjusting images should be about 6 times faster as compared to the LCD according to the related art, and flickering and color break-up of moving pictures occur. Thus, it is not easy to put the FSC LCD technology to practical use.
In addition, Yoichi Taira has invented an edge illumination LCD without a color filter, in which light emitted from a CCFL or a RGB LED array is incident into RGB subpixles by using a lenticular lens array and a prism array structure. However, the edge illumination LCD without the color filter requires a light guide panel and thus, it is not easy to use the technology in a direct lighting type LCD TV that does not include the light guide panel and requires large-scale and high brightness.